This invention relates to dual mode, dielectric resonator, loaded cavity filters and, more particularly, to such filters adapted to radiate via horn radiators in a phased array antenna by provision of metallic annular rings directly on resonator surfaces facing the horn radiators.
Dielectric resonator filters constructed of a series of dielectric resonators enclosed within metallic cavities are employed in situations requiring reduced physical size and weight of the filters. One such situation of interest is in a satellite communication system wherein the filters are to be carried on board a satellite as a part of microwave circuitry of the communication system. The reduced size and weight of such a filter arise because the wavelength of an electromagnetic signal within a dielectric resonator is substantially smaller than the wavelength of the same electromagnetic signal in vacuum or in air. Coupling of electromagnetic power between contiguous cavities may be accomplished by means of slotted irises, as is disclosed in Fiedziuszko, U.S. Pat. No. 4,489,293. The aforementioned United States patent provides details in the construction of such a filter, and is incorporated herein by reference in its entirety. Such filters are capable of operation with circularly polarized electromagnetic signals, the circularly polarized signals being preferred in satellite communication systems. Such filters provide low-loss filtering, and avoid the disadvantage of excessive bulk of low-loss waveguide filters, the excessive bulk of waveguide filters rendering them incompatible with modern planar phased array systems. Furthermore, the dielectric resonator loaded cavity filters are preferred in satellite communication systems over planar stripline type filters because the stripline filters have unacceptably high losses for moderate and narrow bandwidths.
However, in spite of the foregoing advantages of the dielectric resonator filter, a problem arises in coupling signals from the filter to a radiating element of the antenna to attain a high flow of power with good coupling of the electromagnetic circularly polarized signal into the environment external to the radiating element. For example, existing antenna systems, such as those employing waveguide filters operative with circular polarization, accomplish the coupling of power with the aid of bulky components such as septum polarizers and other bulky components. Such use of excessively large and heavy microwave power-coupling circuitry would defeat much of the advantage of small size and weight of the dielectric resonator cavity filter. In particular, there is interest in the HE.sub.11.DELTA. hybrid mode wherein .DELTA. may have any value from 0-1, and represents a portion of the half wavelength of an electromagnetic wave residing in a resonator spaced apart from an enclosing cavity wall. Aperture coupling of the dielectric resonator cavity filter operating in the HE.sub.11.delta. hybrid mode to waveguides or to free space is a problem in that presently available microwave circuitry does not provide adequate coupling.